AIR CONDITIONING SYSTEM BASIC INFORMATION AND TUTORIALS

WHAT IS AN AIR CONDITIONING SYSTEM?


Figure below shows the schematic diagram of an air-conditioning plant. The majority of the air is drawn from
the space, mixed with outside ventilation air and then conditioned before being blown back into the space.

Air Conditioning Plant

Air-conditioning systems are designed to meet a variety of objectives. In many commercial and institutional systems, the ratio of outside ventilation air to return air typically varies from 15 to 25% of outside air. There are, however, systems which provide 100% outside air with zero recirculation.

The components, from left to right, are: Outside Air Damper, which closes off the outside air intake when the system is switched off. The damper can be on a spring return with a motor to drive it open; then it will automatically close on power failure.

On many systems there will be a metal mesh screen located upstream of the filter, to prevent birds and small animals from entering, and to catch larger items such as leaves and pieces of paper. Mixing chamber, where return air from the space is mixed with the outside ventilation air.

Filter, which cleans the air by removing solid airborne contaminants (dirt). The filter is positioned so that it cleans the return air and the ventilation air.

The filter is also positioned upstream of any heating or cooling coils, to keep the coils clean. This is particularly important for the cooling coil, because the coil is wet with condensation when it is cooling.


Heating coil, which raises the air temperature to the required supply temperature.

Cooling coil, which provides cooling and dehumidification. A thermostat mounted in the space will normally control this coil.

A single thermostat and controller are often used to control both the heating and cooling coil. This method reduces energy waste, because it ensures the two coils cannot both be “on” at the same time.

Humidifier, which adds moisture, and which is usually controlled by a humidistat in the space. In addition, a high humidity override humidistat will often be mounted just downstream of the fan, to switch the humidification “off” if it is too humid in the duct.

This minimizes the possibility of condensation forming in the duct.

Fan, to draw the air through the resistance of the system and blow it into the space. These components are controlled to achieve six of the seven air-conditioning processes.

Heating: directly by the space thermostat controlling the amount of heat supplied by the heating coil.

Cooling: directly by the space thermostat controlling the amount of cooling supplied to the cooling coil.

Dehumidifying: by default when cooling is required, since, as the cooling coil cools the air, some moisture condenses out.

Humidifying: directly, by releasing steam into the air, or by a very fine water spray into the air causing both humidification and cooling.

Ventilating: provided by the outside air brought in to the system.

Cleaning: provided by the supply of filtered air.

Air movement within the space is not addressed by the air-conditioning plant, but rather by the way the air is delivered into the space.

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11 comments:

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john wood said...

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